The major hazard faced by both commercial and sport divers is decompression sickness which results from the release of dissolved gases from the body tissues and blood as discrete bubbles when the ambient pressure is reduced too rapidly. As the ambient pressure on a diver is increased during a dive, the body tissues and blood begin to absorb more gas from the breathing mixture to reach equilibrium with the increased pressure. A certain percentage of these dissolved gases must be eliminated by the tissue and blood before the diver can return to the surface. Failing this elimination the diver is liable to extremely grave physiological disorders, known as "the bends," upon surfacing, and these disorders are capable of causing paralysis or even death.
The process of decompression consists in exposing the diver to graduated pressures that are successively lesser than the pressure at which he was diving. These lesser pressures can be achieved by the diver ascending to shallower depths and maintaining these depths for predetermined periods of time in accordance with decompression tables. At the lesser pressures (shallower depths) the dissolved gases come out of solution and are removed by the lungs of the diver. More commonly in commercial diving the diver is rapidly brought to the surface and then placed in a decompression chamber aboard a surface ship or boat. The pressure is successively lowered in the decompression chamber while the diver rests in less hazardous surroundings than the open water.
Underwater diving has proven to be extremely hazardous to the divers and improper decompression is one of the major hazards. Persons in charge of diving crews must have immediate data records of the lengths of time a diver has been exposed to various depths. The greater the depth, the greater the amount of dissolved gases and the greater the hazard from improper decompression. Exact time and depth records are therefore vital to safe diving operations. Additionally, there is a need for a permanent record of the time-pressure exposure of a diver when there has been a decompression accident, so that corrective measures can be taken. Public and private safety officials need such data, and heretofore this has not been available.